Med diet best for heart disease (but some junk food won’t hurt)

"People with heart disease have a lower risk of heart attack and strokes if they eat a Mediterranean-style diet," The Guardian reports.

The study it reports on also suggests that the occasional Western-style treat probably doesn't pose much of a risk for people with heart disease.

After recruiting more than 15,000 people with heart disease from 39 countries, researchers scored their diets for Mediterranean elements such as eating plenty of whole grains, fruits, vegetables, legumes, fish, some alcohol, and some meat. They also scored diets for Western diet elements, such as consumption of refined grains, sweets and desserts, sugared drinks, and deep-fried foods.

After an average of 3.7 years, death, non-fatal heart attack or stroke occurred in 7.3% of people with a Mediterranean score of 15 or more – about 3% less than those scoring 14 or below (around 10%).

Surprisingly for some, higher Western diet scores did not increase the risk of these same problems.

The findings related to a very specific group: adults with stable coronary heart disease (CHD) who were at high risk of having a major cardiovascular event. This means the 3% reduction is not generalisable to the wider population, or even to all people with heart disease.

Some of the reporting promotes the line that "eating good food is more important than avoiding bad food".

Newspapers love a Mediterranean diet

Potential benefits of the Mediterranean diet for cardiovascular health are often in the news. For example, a 2013 study involving around 7,500 people found that sticking to the diet cuts the risk of heart disease and stroke by 30%.

The media reporting was generally accurate, with many focusing on the finding that the Western diet did not increase major risk of cardiovascular events. Only the Guardian acknowledged that the study also pointed to the benefits of the Mediterranean-style diet.

What kind of research was this?

This was a longitudinal study looking at the effect of diet on serious cardiovascular outcomes in adults with CHD.

CHD is the leading cause of death both in the UK and worldwide. It's responsible for more than 73,000 deaths in the UK each year. About 1 in 6 men and 1 in 10 women die from CHD.

What did the research involve?

The study analysed data from adults with stable CHD and a high risk of a major cardiovascular event already recruited to a study, called the STABILITY trial. This was designed to test whether a new drug called Darapladib (not currently licensed in the UK) would prevent major cardiovascular events in this high-risk group. Some of the group were taking Darapladib, while others were taking a placebo.

From the STABILITY trial, the researchers used self-reported lifestyle data from 15,482 people from 39 countries to score each for "Mediterranean diet" elements, like eating plenty of whole grains, fruits, vegetables, legumes, fish, alcohol and some meat. They then scored them for "Western diet" elements, such as consumption of refined grains, sweets and desserts, sugared drinks, and deep-fried foods. People were asked to recall both the type and frequency of food during "a typical week".

They then compared the numbers of major cardiovascular events – defined as death, non-fatal heart attack or non-fatal stroke – over the next three years (median 3.7 years) in those with greater Mediterranean or Western diet scores, to see if they were protective or harmful.

The analysis took account of many confounding factors known to affect risk of major cardiovascular events, including:

The Mediterranean and Western diet scores were totalled and categories defined. For example, most people (56%) scored 12 or less for Mediterranean score, a quarter scored 13 to 14 (26%) and a minority scored 15 or over (18%). Despite the differences in Mediterranean score, Western diet scores were around 12 across all three groups.

What were the basic results?

Those scoring highest for a Mediterranean-style had fewer deaths, non-fatal heart attack or non-fatal stroke over an average of 3.7 years. These events occurred in 7.3% of people with a Mediterranean score of 15 or more – about 3% less than those scoring 13 to 14 (10.5%), or less than 12 (10.8%).

For Mediterranean diet scores less than 12, there was no link between increase in score and fewer major cardiovascular events.

But for every point increase on the Mediterranean style diet score over 12, the risk of death, non-fatal heart attack or stroke lowered by 5% (hazard ratio [HR] 0.95, 95% confidence interval [CI] 0.92 to 0.99).

There was no corresponding link between higher Western diet scores and deaths, non-fatal heart attack or strokes over the same period, which was not what the researchers had expected.

How did the researchers interpret the results?

The researchers' conclusion was refreshingly simple: "Greater consumption of healthy foods may be more important for secondary prevention of coronary artery disease than avoidance of less healthy foods typical of Western diets."

They also point out the diet is not specific to Mediterranean countries, and is similar to the diet already recommended to people to stop high blood pressure, and is recommended in broader national dietary guidelines.

Conclusion

This study showed 3% fewer people with CHD, at high risk of major cardiovascular events, who reported eating the healthiest Mediterranean-style diets, had either died, or had a non-fatal heart attack or stroke over a three-year period than those with less healthy diets. Western diet scores were not related to major cardiovascular events.

The study was large, worldwide and its methods quite robust, all boosting the believability of the findings.

It is possible that unmeasured factors explain all or part of the findings, but the study made a concerted attempt to minimise the chance of this through adjusting for important confounders in their analysis.

Only around 18% of the 15,000 or so studied fell into the Mediterranean-style diet group that showed health benefits; the same link wasn't found in lower-scoring groups. This suggests that most of those studied could potentially benefit from a healthier diet.

It is important to realise that the findings relate to a very specific group: adults with stable CHD who were at high risk of having a major cardiovascular event. The group was even more uncommon than this, as some were also taking an experimental drug called Darapladib as part of a separate study; this reportedly had little impact on the diet-related findings. Therefore, the 3% reduction figure does not apply to the general population, or even to all people with CHD.

That is not to say that a healthy diet won't benefit the wider population – it probably will, but this study didn't look at this or provide a figure of the magnitude of benefit.

What is more applicable to the masses is the clear implication of the study. That a diet high in whole grains, fruits, vegetables, legumes, fish, some alcohol, and lower in meat, has health benefits. This is nothing new and is already incorporated into most healthy lifestyle recommendations and diet advice for people looking to lower their risk of high blood pressure. What the study does add is a quantification of the benefit of a good diet in a specific high-risk group.

Interestingly, higher scores for a Mediterranean diet were more common in the Asia/Pacific and Northern Europe regions than Mediterranean countries themselves. It seems people living in, for example, Japan or Norway are more likely to follow a traditional Mediterranean diet than people living in the Mediterranean.

The finding that a higher Western diet score – usually associated with worse heart health – was not linked to major cardiovascular events was more surprising. These new data suggest, as the study authors put it: "Greater consumption of healthy foods may be more important for secondary prevention of coronary artery disease than avoidance of less healthy foods typical of Western diets."

That shouldn't be taken as a green light to start chugging down the cheeseburgers, especially if you have a history of heart disease. The saying, "the absence of evidence is not the same as evidence of absence" may be clichéd, but like most clichés, it contains an element of truth.

It could be the case that a larger study with a more generalised population could find a link between Western-style diet and increased risk of serious cardiovascular events.